1. Field of the Invention
The present invention relates to an optical lens for image pickup, and more particularly to the optical lens for image pickup comprised of five lens elements with great image quality for applying to electronic products.
2. Description of the Related Art
In compact electronic products such as digital still cameras or mobile phone cameras, an optical lens for image pickup is generally installed for capturing images of an object, and the optical lens for image pickup tends to be developed with a compact design and a low cost, while meeting the user requirements for good aberration correction ability, high resolution, and high image quality.
In general, a conventional optical lens for image pickup of a compact electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. However, if the imaging quality is taken into consideration, the optical lens for image pickup with the four-lens or five-lens designs has advantages on image aberration and modulation transfer function (MTF) performance.
In various compact designs of the five-lens optical lens for image pickup having a fixed focal length, the prior arts adopt different combinations of positive and negative refractive powers. As disclosed in U.S. Pat. No. 7,663,813 which adopts a group of stacked lens elements, in which the two cemented glass lenses incur a higher manufacturing cost, and such conventional optical lens for image pickup is unfavorable for the cost control of mass production. Another conventional technique is the combination of a first lens element with negative refractive power and a second lens element with positive refractive power as disclosed in U.S. Pat. No. 7,480,105, but such conventional optical lens for image pickup cannot reduce the total length of the optical system easily to meet the requirement of the compact design.
Therefore, the present invention provides a more practical design to shorten the optical lens for image pickup, while using a combination of refractive powers and a combination of convex and concave surfaces of five lens elements to lower the cost for mass production easily and apply the optical lens for image pickup to compact electronic products.